Add netbox_rack_concept plugin: rack blueprint planning

Introduces a NetBox 4.6 plugin for planning rack layouts (RackConcept,
ConceptDevice) without creating real dcim.Rack/dcim.Device objects, so
blueprints never appear in rack/device lists, utilization reports, or
IPAM.

Features:
- Copy paths: real rack -> concept, concept -> concept (clone), and
  concept -> one or more real racks (deploy, with name patterning and
  dry-run support)
- Manual concept creation via a dedicated "Rack Concepts" nav menu
- Tenant and tenant group assignment on concepts and planned devices
- Partial-width device placement (1/1-1/4) with slot-based collision
  detection, matching netbox_utilities' partial-width feature
- Custom drag-and-drop elevation (netbox-reorder-rack operates on real
  Device querysets, which concepts don't have) with server-side
  validation of every move
- Full REST API, filtering, CSV import, bulk edit, search integration
- Optional, config-driven interop with netbox_utilities (partial-width
  field mapping) and netbox-reorder-rack, degrading gracefully when
  either plugin is absent

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,31 @@
+[build-system]
+requires = ["setuptools>=68", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "netbox-rack-concept"
+version = "0.1.0"
+description = "Rack blueprints for NetBox: plan racks and their equipment without creating real racks or devices"
+readme = "README.md"
+requires-python = ">=3.12"
+license = { text = "MIT" }
+authors = [{ name = "Louis" }]
+keywords = ["netbox", "netbox-plugin", "dcim", "planning"]
+classifiers = [
+    "Framework :: Django",
+    "Programming Language :: Python :: 3.12",
+    "Intended Audience :: System Administrators",
+]
+
+[project.urls]
+Homepage = "https://github.com/example/netbox-rack-concept"
+
+[tool.setuptools.packages.find]
+include = ["netbox_rack_concept*"]
+
+[tool.setuptools.package-data]
+netbox_rack_concept = [
+    "templates/netbox_rack_concept/*.html",
+    "templates/netbox_rack_concept/inc/*.html",
+    "static/netbox_rack_concept/*",
+]